Catheters including balloons are routinely used to resolve or address flow restrictions or perhaps even complete blockages in tubular areas of the body, such as arteries or veins. In many clinical situations, the restrictions are caused by hard solids, such as calcified plaque, and may sometimes involve the use of high pressures to compact such blockages. Commercially available balloons employ complex technology to achieve high pressure requirements without sacrificing the profile of the balloon. Besides high pressure requirements, the balloons should also be resistant to puncture, easy to track and push, and present a low profile, especially when used for angioplasty.
In clinical practice, an angioplasty balloon 12 may be expanded from a deflated, folded state (FIG. 1) to an inflated, expanded state (FIG. 2) within a vessel at a treatment area T, such as a portion of the circumferential inner wall of a blood vessel V. The inflation may be completed using an X-ray contrast agent or media CM filling the balloon 12 to a height DX to provide better visibility under X-ray energy XR or other form of radiography during the interventional procedure, as illustrated in FIGS. 3 and 4. Typically, a 70/30 percent mixture of contrast agent and saline is used to inflate the balloon during an angioplasty procedure.
In general, a desirable goal is to reduce inflation and deflation times required for balloons without sacrificing the profile of the balloons, especially for large volume balloons (which can require up to two minutes of inflation/deflation times with the contrast agent). Because of its relatively high viscosity, it would also be desirable to eliminate, or at least reduce the amount of, the contrast agent used in inflation/deflation of the balloons. The use of contrast agent prolongs the inflation/deflation times and also poses the risk of iodine exposure to patients sensitive to iodine. In this regard, a non-radiopaque substance could be used in lieu of the contrast agent, such as for example saline or carbon dioxide, but such substances are invisible during X-ray imaging, and thus do not help with locating the balloon 12 in the desired manner.
Furthermore, the clinician performing the angioplasty procedure should be able to locate the position of the uninflated balloon with accuracy, so that the balloon will be properly positioned once inflated. This is conventionally accomplished by attaching marker bands on the catheter shaft corresponding to the ends of the balloon working surface. This “working surface” is the surface along the portion of the balloon that is used to achieve the desired treatment effect, such as contacting the calcified plaque (which surface in the case of a balloon having conical or tapering sections at the proximal and distal ends is typically co-extensive with a generally cylindrical barrel section).
Misalignment of the marker bands during placement along the shaft sometimes results in their failure to correspond precisely to the extent of the working surface, as is shown in FIG. 5 (note misalignment amount X between each interior marker band serving as marking M carried by shaft S and working surface W of balloon 12, which also typically includes a radiopaque tip P at the distal end). Even upon exercising great care to position the markings properly on the underlying shaft in alignment with anticipated boundaries of the working surface when the balloon is inflated, a tendency for mismatch remains due to several possible factors. One such factor may be the tolerance stack-ups arising as a consequence of the affixation of the balloon to the distal end of the catheter shaft. The balloon also has a tendency to grow in the longitudinal direction when inflated, especially with large and particularly long balloons. Another factor is the tendency of the portion of the catheter shaft within the balloon to bend or flex during inflation. This may lead to mis-alignment between markings M fixed to the shaft S and the working surface W.
Whatever the cause, the resulting misalignment may prevent the clinician from accurately identifying the location of the working surface of the balloon during an interventional procedure. This may lead to a geographic misplacement, or “miss,” of the intended contact between the treatment area and the working surface of the balloon. It is especially desirable to avoid such an outcome when the balloon is designed to deliver a payload (such as a drug, stent, or both) or a working element (such as a cutter, focused force wire, or the like) to a specified location within the vasculature, since a miss may prolong the procedure (such as, for example, by requiring redeployment of the balloon or the use of another balloon catheter in the case of a drug coated balloon).
In order to assess the length of a lesion from a location external to the body, a clinician may also use an external ruler, which in one form is called a “LeMaitre” tape. While the use of such a ruler or tape may allow for a more precise assessment of the lesion length and an area treated by a pre-dilatation step, it is not without limitations. For one, a displacement or difference in the apparent position of the lesion margins results when viewed along two different lines of sight. This “parallax” can lead to an inaccurate measurement and, at a minimum, contribute to the geographic misalignment of the working surface relative to the lesion. The use of such an external ruler may also lead to inferior measurements when the vasculature at issue is particularly tortuous.
Accordingly, there is a need for a balloon for which the working surface may be identified during an interventional procedure with enhanced precision. One solution would take into account the possible mismatch between fixed locations on the catheter shaft and the balloon to define the working surface. Another would provide for a manner in which to position a balloon catheter into the vasculature at a treatment area with enhanced accuracy. Overall, procedural efficiency would be enhanced without remarkably increasing cost or complexity, and in a manner that can be applied to many existing catheter technologies without extensive modification.